Caffeine increases the velocity of rapid eye movements in unfatigued humans
Caffeine is a widely used dietary stimulant that can reverse the effects of fatigue on cognitive, motor and oculomotor function. However, few studies have examined the effect of caffeine on the oculomotor system when homeostasis has not been disrupted by physical fatigue. This study examined the influence of a moderate dose of caffeine on oculomotor control and visual perception in participants who were not fatigued.
Within a placebo-controlled crossover design, 13 healthy adults ingested caffeine (5 mg·kg−1 body mass) and were tested over 3 h. Eye movements, including saccades, smooth pursuit and optokinetic nystagmus, were measured using infrared oculography.
Caffeine was associated with higher peak saccade velocities (472 ± 60° s−1) compared to placebo (455 ± 62° s−1). Quick phases of optokinetic nystagmus were also significantly faster with caffeine, whereas pursuit eye movements were unchanged. Non-oculomotor perceptual tasks (global motion and global orientation processing) were unaffected by caffeine.
These results show that oculomotor control is modulated by a moderate dose of caffeine in unfatigued humans. These effects are detectable in the kinematics of rapid eye movements, whereas pursuit eye movements and visual perception are unaffected. Oculomotor functions may be sensitive to changes in central catecholamines mediated via caffeine’s action as an adenosine antagonist, even when participants are not fatigued.
KeywordsOculomotor control Eye movements Caffeine Saccades Smooth pursuit Optokinetic nystagmus Visual perception
We thank the participants who volunteered their time to take part in the study. We are grateful to Hayden Green for his assistance in data collection.
Conceptualization: C.J.W.C., B.T. and N.G.; methodology: C.J.W.C., B.T. and N.G.; software: C.J.W.C., J.T. and R.H.; formal analysis: C.J.W.C.; investigation: C.J.W.C.; resources: N.G.; writing—original draft: C.J.W.C.; writing—review and editing: C.J.W.C., N.G. and B.T.; supervision: N.G.
Compliance with ethical standards
The authors have no competing financial interests to declare.
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